Valproic Acid-Induced Upregulation of Multidrug Efflux Transporter ABCG2/BCRP via PPARa-Dependent Mechanism in Human Brain Endothelial CellsS

Despite the progress made in the development of new antiepileptic drugs (AEDs), poor response to them is a rising concern in epilepsy treatment. Of several hypotheses explaining AED treatment failure, the most promising theory is the overexpression of multidrug trans-porters belonging to ATP-binding cassette (ABC) transporter family at blood-brain barrier. Previous data show that AEDs themselves can induce these transporters, in turn affecting their own brain bio-availability. Presently, this induction and the underlying regulatory mechanism involved at human blood-brain barrier is not well eluci-dated. Herein, we sought to explore the effect of most prescribed first-and second-line AEDs on multidrug transporters in human cere-bral microvascular endothelial cells, hCMEC/D3. Our work demon-strated that exposure of these cells to valproic acid (VPA) induced mRNA, protein, and functional activity of breast cancer resistance protein (BCRP/ABCG2). On examining the substrate interaction sta-tus of AEDs with BCRP, VPA, phenytoin, and lamotrigine were found to be potential BCRP substrates. Furthermore, we observed that siRNA-mediated knockdown of peroxisome proliferator-activated re-ceptor alpha (PPARa) or use of PPARa antagonist, resulted in attenuation of VPA-induced BCRP expression and transporter activ-ity. VPA was found to increase PPARa expression and trigger its translocation from cytoplasm to nucleus. Findings from chromatin immunoprecipitation and luciferase assays showed that VPA enhan-ces the binding of PPARa to its response element in the ABCG2 pro-moter, resulting in elevated ABCG2 transcriptional activity. Taken together, these in vitro findings highlight PPARa as the potential mo-lecular target to prevent VPA-mediated BCRP induction, which may have important implications in VPA pharmacoresistance.SIGNIFICANCE STATEMENTInduction of multidrug transporters at blood-brain barrier can largely affect the bioavailability of the substrate antiepileptic drugs in the brains of patients with epilepsy, thus affecting their therapeutic effi-cacy. The present study reports a mechanistic pathway of breast cancer resistance protein (BCRP/ABCG2) upregulation by valproic acid in human brain endothelial cells via peroxisome proliferator-activated receptor alpha involvement, thereby providing a potential strategy to prevent valproic acid pharmacoresistance in epilepsy.